Swimming motion of a singly flagellated bacterium close to a rigid surface was numerically investigated. The cell’s attitude and its distance from the surface were calculated by integrating the velocity and angular velocity determined by the boundary element analysis at an instant. A diagram indicating the transition of the cell’s state that was defined as a couple of the pitch angle and the distance was obtained. Four separated regions exist on the diagram for an average size cell. When the absolute of the pitch angle is bigger than a certain threshold value, the cell monotonically leaves from the surface, or approaches and touches the surface. With a moderate pitch angle, the state for forward motion converges to a point, while the state for backward motion diverges since the state of backward motion conversely follow the same transition path. The observed asymmetry between forward and backward motions is explained according to the diagram.
2010 by The Japan Society of Mechanical Engineers